How do I find where the antifreeze going in my 1998, 5.7 silverado, the oil is not milky, no white smoke out of exhaust, no puddles on the floor?

SOURCE: 99 Chev suburban 5.7 liter, antifreeze keeps

check the condition of the reserve tank and the hose from the reserve tank to the radiator for leaks if no leaks there have the Radiator cap presure tested . also this could be a air lock in the engine if the radiator is new with the engine running and the heater on hot observe the fluid level in the radiator with the cap off if it drops as it warms add more coolant this will purge the air .

SOURCE: 2001 chevy silverado 5.3 ltr I am adding 1 gallon

This is one that you will need to do some careful looking to find. every hose connection needs to be looked at for damp residue as well as all gasket parting lines (thermostat housing, head to block parting lines, intake manifold ends etc.) You may also need to have a shop to a radiator pressure test as well as a cylinder leakdown test (which will pick up on most internal leaks) If seepage is very minor, coolant can burn off or boil out before reaching a noticeable level inside the engine or even at a gasket to the outside. A small crack between the valves in a cylinder head can be so small that it goes unnoticed when exiting along with exhaust. A small leak now may be difficult to find but locating it now is better than waiting for a larger failure. It may turn out to be something simple as a bad cap on the radiator or the shaft seal beginning to fail on your water pump...letting it go can eventually cost you an engine.

rtpflh

• 546 Answers
• Posted on Oct 05, 2009

SOURCE: 2001 CHEVY SILVERADO 5.3 Z71 The truck uses 1 gal of antifreeze

check for a wet tailpipe,which might indicate a leak between water jacket & combustion chamber.i.e.headgasket.check heater hose isn't leaking onto exhaust manifold,'cooking' the anti-freeze as it leaks.

SOURCE: if my car has some white smoke coming out the tail

If you have steady thick white smoke and it smells like anti freeze it is most likely the head gasket. The head gasket can fail in different areas. If it has white smoke it failed between a coolant passage and the combustion chamber. If the oil is milky it failed between the coolant passage and an oil passage. Just because the oil isn't milky doesn't necessarily mean that the head gasket it's blown.

SOURCE: Have some white, milky looking substance on the dip stick

I'd be tempted to live with it depending on whether the vehicle is using coolant on the assumption that it is condensation causing the saponification of the oil. If the Lucas oil treatment caused the pressure to rise so dramatically I would suspect that some crud has come adrift and lodged in the pressure sender.
The chance that the cylinder head is cracked would be more rare than a leaking head gasket both of which could possibly be tested by a leakdown test of individual cylinders.
The water has to come from somewhere.
Does the soap go away when the engine is warmed up?

Testimonial: "Good point on the pressure issue, not using coolant. Dip stick had rust on it and so did the inside of the fill cap. Hot or cold white on the stick."